Consider a high frequency signal, particularly one in a short wavelength frequency band, such as an extremely high frequency (EHF) wave. When such a signal is to be emitted from or received by an antenna using a transmitter circuit or a receiver circuit, the signal is converted from the transmitter circuit signal format, which is used between the transmitter circuit and the antenna as well as between the receiver circuit and the antenna, to a hollow waveguide signal propagation mode. Alternatively, the signal may be converted from the hollow waveguide signal propagation mode to the receiver circuit signal format. A signal converter is used for such signal conversion.
There exist several proposed structures for coupling a circuit chip or similar device that constitutes the transmitter circuit and receiver circuit with a waveguide. For example, the structure proposed in Japanese Laid-open Patent Publication No. 2003-289201 is provided with a first resonator that connects to a hollow waveguide, and a second resonator that couples with the first resonator. In such a structure, the end of a post-wall waveguide at the first resonator is closed by an array of through conductors, and a coupling window for connecting with the hollow waveguide is provided. The first and second resonators are formed by narrowing the H-plane of the post-wall waveguide at a predetermined interval.
As another example, in the structure proposed in Japanese Laid-open Patent Publication No. 2000-244212, a shorting metal layer is provided on one face of a dielectric substrate, while on the other face there is provided a grounding metal layer in the same shape as the aperture cross-section of a hollow waveguide. Electric potentials are kept equal by the grounding metal layer, the shorting metal layer, and metal embedding the waveguide in the dielectric substrate. In this case, a matching element is installed on the front face of the dielectric substrate enclosed by the grounding metal.
As another example, in the structure proposed in Japanese Laid-open Patent Publication No. 2008-131513, a first ground layer is provided on one face of a dielectric substrate, while a second ground layer is provided on the other face. A hollow waveguide is provided on the side of the first ground layer, and a patch is provided in a notch of the first ground layer.
As another example, in the structure proposed in Japanese Laid-open Patent Publication No. 2006-295891, first and second dielectric substrates are provided, with an hollow coupling conductor for a coplanar strip transmission line installed on the first dielectric substrate, and with a ground conductor installed on the second dielectric substrate.